Shortstopping vinyl chloride polymerizations with ethylenically-unsaturated ketones



Patented Nov. 4, 1952 2,616,881 7 SHORTSTOPPING VINYL CHLORIDE POLY- MERIZATIONS WITH ETHYLENICALLY- UNSATURATED KETONES Dexter C. Seymour, .Wyckoif, N. J., assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey No Drawing. H Application July 10, 1951, Serial No. 236,062

Claims.

This. invention relates to improvements .in vinyl chloride polymerizations.

The polymerization of liquefied vinyl chloride is generally carried out at mildly elevated temperatures, about 40 C. to 60 C., in an aqueous medium under a pressure substantially equal to its saturated vapor pressure, i. e. about 4 to 9 atmospheres, in the presence of a polymerization catalyst. Pressures referred to herein are absolute pressures. The polymerization is generally carried to a range of about 60% to 95% conversion of monomer to polymer. Percent.- ages and parts referred to herein are by weight. The polymerization as is Well known may ..be an emulsion polymerization (see Mark et al. U. S. Patent 2,068,424, and German Plastics Practice by DeBell, Goggin & Gloor, Pub.1.by

DeBell and Richardson, Springfield, Mass, 1946, pages 57-66), or a granular polymerization (see Lightfoot U. S. Patent 2,511,593, and German Plastics Practice, pages 66-73, and the article by Ruebensaal. on Vinyl Resins" in Chemical Engineering for December 1950, vol. 57, pages 102 to 105). After conversionof the desired amount of monomer to polymer, residual-unreacted monomeric vinyl chloride is removed and the polyvinyl chloride collected by various means, such as by coagulation or spray drying in the case of aqueous emulsion polymerization, or by filtration in the case of aqueous granular polymerization. The resulting polyvinyl chloride is usually washed with water and dried. If the polymerization goes beyond the desired conversion, a polymer having properties inferior to those desired in the final product may result,. particularly as regards heat and light stability. To avoid this, the batch is generally cooled after the desired conversion. Undesirable post-polymerization may also take place in'the blowdown tank. orin the stripper where unreacted vinyl chloride monomer is removed. At the end of the polymerization, it may be necessary to store or hold the polymer batch for some time without cooling before removing unreacted vinyl chloride monomer. In this case the polymerization may continue during storage and thus give a product of too high conversion and of resultant undesirable properties. Also, when the, unreacted vinyl chloride monomer is removed from the aqueous medium, there may be some vinyl chloride monomer, adsorbed on the polyvinyl chloride particles in the aqueous medium, which is not removed until drying of the polyvinyl chloride. This absorbed vinyl chloride monomer may polymerize on the polyvinyl chlo-.

2 ride particles before it can be removed, adversely afiecting the properties of the finally recovered polyvinyl chloride. It is therefore desirable to add a material which acts to terminate or shortstop the vinyl chloride polymerization reaction after the desired partial conversion of polymerizable monomer to polymer has taken place and to prevent any further polymerization of the residual unreacted vinyl chloride monomer.

I have found that alpha-alkyl-alpha, betaunsaturated ketones are effective shortstopping agents for vinyl chloride polymerizations.

In carrying out the present invention, the alpha-alkyl-alpha, beta-unsaturated ketone is added to the polymerization reaction after partial conversion of polymerizable monomer to polymer (usually after about to'95% conversion) and thereafter the unreacted vinyl chloride polymer is removed from the aqueous medium, and. the polyvinyl chloride recovered'in the usual manner. Examples of alpha-alkylalpha, beta-unsaturated ketones that may be used are methyl isopropenyl ketone, 4-ethoxy-3- methyl 3 butene 2 one, 3 methyl 4- phenyl 3 butene 2 one, 3 ethyl 3 pentene 2 one, 3.4 dimethyl 3 pentene- 2 one, and mixtures thereof. Very small amounts of such unsaturated ketones may satisfactorily be used to shortstop the polymerization reaction, the amount efiective to shortstop the polymerization generally being less than 2% based on the original vinyl chloride monomer used. For practical purposes, the amount of shortstopper may be between 0.05% and 1% by weight of the original vinyl chloride monomer used.

The polymerization reaction is carried out in the presence of a conventional free radical type polymerization initiator, such as a perox'ygen or azo catalyst. Examples of peroxygen catalysts are inorganic peroxides, e. g. hydrogen peroxide and persalts, such as alkali persulfates, alkali perborates, alkali percarbonates; and organic peroxides, e. g. diacetyl peroxide, dibenzoyl peroxide, acetyl benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, tertiary butyl hydroperoxide. Examples of azo catalysts are alpha, alpha azobisisobutyronitrile, and pmethoxybenzene diazo thi0-2-naphthyl etherr Catalytic amounts from 0.05% to 2% basedron the vinyl chloride monomer may be used;

Tests showing the eiiectiveness of the chemicals of the present invention as short'stopping agents. for vinyl. chloride polymerization were carried out according to the following procedure:

3 Into a Carius pressure tube was weighed 0.5328 g. (0.00325 mole) of catalyst (alpha, alphaazobisisobutyronitrile) and the tube was sealed to a vacuum line. After evacuation to 0.0001 mm., 20.00 cc. (19.94 g., 0.319 mole, volume measured at 30 C.) of pure vinyl chloride was distilled in and the tube was sealed off and heated at 30 C. for 4.5 hours. At the end of this time the contents were. frozen in liquid nitrogen, the tube was opened, sealed to the" vacuum line and evacuated. The unreacted vinyl chloride was distilled into a buret and its volume at 30 C. noted. From this was calculated the percent conversion before adding shortstop. Meanwhile, the tube was removed from the vacuum line and to it was added one weight percent on the original vinyl chloride of the chemical under test as a shortstop. The tube was rescaled to the vacuum line, its unreacted vinyl chloride was replaced, the tube was sealedan under vacuum and heated again at"30 'C'. 'for4:5 hours. After the second heating period the tube was frozen, opened and sealed to the line as before. A final measurement Ofthef volume of unreacted vinyl chloridewas made and 'the percent conversion after adding shortstop'was calculated. The difference between these two conversions was taken as a measure of the shortstoppingxpower of the compound undeninvestigation. A control run without shortstop was carried out as a means of comparison. Results of these tests are shown in the following table:

L a Percent Con- Chemical Added after Perceglt g Percept version In- 4.5 hrs. i 3 f 5 8 crease in Final'4.5 hrs.

Mthyl-lsopropenyl ke-- .tone 15.6 1548; 0. 2 None (control) 17. 2 37; 3 20.1

agitated in a'cons'tantt'emperature bath at 45 C. for about "7 hours, at which time analyses showed a'conversion of monomer to polymer of approximately 60%. At this point 015 part of methyl is'opropenyl "ketone was added to one or the reaction vessels and no chemical was added to the othervessel (control polymerization). The agitation .of the vessels i'n'the 45 C. bath'was continued for hoursmore. At the end" of this; time analysis showed no'increa'se mthe 60% conversion where the methyl isopropenyl- 'ketone fh'ad been added, and; substantially 100% conversion in -the case ofthe control where" noshortstop had been added.

, The above workshows the effectiveness of the chemicals as shortstopping agents i'n the diflicultly shortstop'p'ed early stages 'of'bulk or mass oil-phase vinyl'chloride polymerization, aridin emulsion polymerization. The chemicals of the present invention are also effective as soluble catalyst are ''-generally considered to. be

In fact,v

mass polymerizations of the individual liquid monomer globules. In aqueous emulsion and granular polymerizations, the polymerization reaction is generally stopped at 60% to conversion of monomer to polymer. In bulk polymerizations, the polymerization reaction is generally stopped at lower conversions, e. g., around 40%. With the shortstoppingagents of the present invention, the polymerization reaction may be stopped at any desired conversion.

In emulsion polymerizations, it is a simple 'matter to withdraw a sample from the reaction chamber from time to time and to analyze it for total solids in order to determine the percent conversion. On the other hand, it is almost impossible to follow the conversion in a granular v polymerization by sampling, because the polymer formed separates so rapidly that a representative sample cannot be obtained. Thus other methods of determining the amount of conversion, and thereby the point at which the reaction should be stopped, must be used in following polyvinyl chloride granular polymerizations. For example, the heat evolved in the reaction mixture can be measured and be directly correlated with the extent of conversion via the known heat of reaction. Also, experience has shown that polyvinyl chloride of good physical characteristics may be obtained by stopping the'reaction-at the pressure drop which is at the point where the separate phase of liquid vinyl chloride'monomer disappears (seeGerman Plastics Practice, pages 61 and '77). In-systems where the temperature. in the; reactor is automatically maintained. by regulation of the jacket temperature, the pressure drop will be evidenced by a sudden-pressure'- fall. Insystems where the pressure hr the reactor'is automatically maintained by regulation of the jacket temperature, the -pressure drop will. be evidenced by a rapid rise ature, whereupon the system is throwncut of automatic control. and coolingwater is .introduced'into the jacket resulting in the usual fall of pressure in the reactor. Such methods other than sample analyses of determining when to shortstop the reaction at the desired conversion may be used in emulsion-polymerizationwas well as in granular polymerization. The evolution or heat-or the viscosity"characteristics may be followed in mass polymerization -to' determine the point at which the 'shortstopping agent should be added. 7 v

The following illustrates'theuse-of the shortstoppers of the present invention in batch aqueous vinyl chloride polymerizations. A typical emulsion polymerization recipe which uses a water soluble catalyst parts of liquefied sulfate, and a small amount of buffering and wetting agents), or a typical granular polymerization recipe using amonomer soluble catalyst (100 parts of liquefied' vinyl-chloride. 300 par'ts of water, 0.5 part 'of- 'lauroyl peroxide and a small amount of suspending agent) is agitated The'batchin a closed jacketed reaction vessel. is initially'heated to the desired re'action temperature between 40" G.- and 60 C. and maintained. at. the desired temperature.- during the polymerization; The-pressure in the reactor at in jacket water temper'-.

such'reaction temperatures will be from 4 to 9 atmospheres until the liquid vinyl chloride is polymerized and the pressure drops. Afterthe pressurestarts to drop and before it drops 2 atmospheres, 0.05 to 1 part of methyl isopropenyl ketone, 4 ethoxy- 3 -methyl -3 butene- 2 one, 3 methyl 4 phenyl 3 butene 2 one, ,3"-ethyl-3-pentene-2-one, or 3,4-dimethyl-3-pentene-Z-one per 100 parts of original vinyl'chloride used is added so that undesirable further polymerization is prevented. Alternatively, the shortstopping agent may be added at any desired conversion at the discretion of the operator. When the desired conversion has been reached and the shortstop added, the batch may be transferred to the blow-downor storage tank, held there any desired length of time, and then transferred to the stripper when desired for removal of residual unreacted vinyl chloride monomer. monomer removal are conventional as described inthe literaturereferences referred to above. 'I-l'ie'shortstopping agents of the present invention give a greater uniformity of polymer properties, and also result in polymers having enhanced heat and light stability.

The shortstoppers of the present invention are applicable to shortstopping of modified vinyl chloride polymers which are made by copolymerizing a major proportion, generally over 80% of vinyl chloride and up to of other monoolefinic material which is copolymerizable with vinyl chloride, such as a vinyl alkanoate, e. g. vinyl acetate, or vinylidene chloride, or an alkyl acrylate, e. g. methyl acrylate, or an alkyl alkacrylate, e. g. methyl methacrylate, or an alkyl maleate, e. g. dimethyl maleate, diethyl maleate, isobutyl maleate, and mixtures thereof. Such polymerizations are similar to the homopolymerization of polyvinyl chloride but with a somewhat broader range of reaction temperatures from C. to 100 0., depending on the particular vinyl chloride copolymer being made (see German Plastics Practice, pages 76-78). The same amount of shortstopping agent based on the amount of vinyl chloride employed may be added after partial conversion, generally at about 60% to 95% conversion of polymerizable monomeric material to polymeric material. 7

In view of the many changes and modifications that may be made without departing from the principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of the protection afforded the invention.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. In the process of preparing a vinyl chloride polymer by the polymerization of material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride,the step comprising adding a small amount of alpha-alkyl-alpha, beta-unsaturated ketone to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material.

2. In the process of preparing a vinyl chloride polymer by the polymerization of material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other monoolefinic material Finishing operations after residual 6 which is copolymerizable with vinyl chloride, the step comprising adding a small amount of alpha-alkyl-alpha, beta-unsaturated ketone selected from the group consisting of methyl isopropenyl ketone, -4-ethoxy-3-methyl-3-butene- 3. In the process of preparing a vinyl chloride polymer by the polymerization of material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride, the step comprising adding a small amount of methyl isopropenyl ketone to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material. 4. Inthe process of preparing polyvinyl chlo ride by the polymerization of vinyl chloride in an aqueous medium, the step comprising adding 0.5% to 1% of alpha-alkyl-alpha, beta-unsaturated ketone based on the weight of the mono-'- meric vinyl chloride being used to the reaction mixture during polymerization to stop the same after about 60% to conversion of vinyl chloride monomer to polyvinyl chloride.

5. The method of preparing a vinyl chloride polymer which comprises subjecting material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other monoolefim'c material which is copolymerizable with vinyl chloride to polymerizing conditions in an aqueous medium in the presence of a polymerization catalyst, and after about 60% to 95% conversion of polymerizable monomeric material to polymeric material adding to the polymerization reaction 0.05% to 1% based on the weight of the original monomeric vinyl chloride used of alpha-alkyl-alpha, beta-unsaturated ketone to stop polymerization of unreacted polymerizable monomeric material, and thereafter removing unreacted polymerizable monomeric material from the aqueous medium.

6. The method of preparing a vinyl chloride polymer which comprises subjecting material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride to polymerizing conditions in an aqueous medium in the presence of a polymerization catalyst, and after about 60% to 95% conversion of polymerizable monomeric material to polymeric material adding to the polymerization reaction 0.05% to 1% based on the weight of the original monomeric vinyl chloride used of alpha-alkyl-alpha, beta-unsaturated ketone selected from the group consisting of methyl isopropenyl ketone, 4-ethoxy-3-methyl-3-butene-2- one, 3-methyl-4-phenyl-3-butene-2-one, 3-ethyl- 3-pentene-2-one, and 3,4-dimethyl-3-pentene-2- one to stop polymerization of unreacted polymerizable monomeric material, and thereafter removing unreacted polymerizable monomeric material from the aqueous medium.

7. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in an aqueous medium in the presence of a peroxygen catalyst, and

afterpartial conversion of vinyl; chloride monomer to-polyvinyl chloride. adding to. the polymerization reaction a small amount *of 'alphaalkyl-alpha, beta-unsaturated ketone to stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride fromthe aqueous medium.

8. The; method-of preparing polyvinyl chloride which comprises subjecting vinyl: chloride to1polymerizing conditions. in-a closed vessel in an aqueous medium at a temperature-between 40 C. and, 60 C. under a pressure substantially equalto itssaturated. vapor pressure of. about: 4 t0 9- atmospheres, and after the. pressure 7 begins todrop and before it has-dropped-Z atmospheres adding. to the polymerization reaction a small amount of alpha-alkyl-alpha, beta-unsaturated ketone tostop polymerization of unreacted vinyl chloride monomer, and. thereafter removing un reacted vinyl chloride from, theaqueouamedium.

, 9. The methodof preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in a closed vessel in an aqueous medium ata temperature-between 40 C. and-60 C. undera pressure substantially equal toi-tssaturated vapor pressure of about 4 to 9 atmospheres, and after the pressure. begins to drop and before it hasdropped-z atmospheres adding to the. polymerization :reaction :a small amount. I of alpha-alkyhalpha, beta-unsaturated ketoneselected from the. group -consisting of methylisopropenyl-ketone,4r-ethoxy-3-methyl 3- butene-Z-onmv '3 methy1 --4 -.pheny1-3-b,utene-2.- one; 3.-ethyl-3'-pentene-2 -one, and 3,4-din iethy1- 3-.epentene-2 one to stop polymerization" of -unreacted vinyl chlorid monomer,; and thereafter removing-unreactedwinyl chloride. from-the aque,-

-DEXTER C. SEYMOUR.

No'refer'ences cited. 

2. IN THE PROCESS OF PREPARING A VINYL CHLORIDE POLYMER BY THE POLYMERIZATION OF MATERIAL OF THE GROUP CONSISTING OF VINYL CHLORIDE AND MIXTURES OF VINYL CHLORIDE WITH UP TO 20% BY WEIGHT OF THE VINYL CHLORIDE OF OTHER MONOOLEFINIC MATERIAL WHICH IS COPOLYMERIZABLE WITH VINYL CHLORIDE, THE STEP COMPRISING ADDING A SMALL AMOUNT OF ALPHA-ALKYL-ALPHA, BETA-UNSATURATED KETONE SELECTED FROM THE GROUP CONSISTING OF METHYL ISOPROPENYL KETONE, 4-ETHOXY-3-METHYL-3-BUTENE2-ONE, 3-METHYL-4-PHENYL-3-BUTENE-2-ONE, 3ETHYL-3-PENTENE-2-ONE, AND 3,4-DIMETHYL-3-PENTENE-2-ONE TO THE REACTION MIXTURE DURING POLYMERIZATION TO STOP THE SAME AFTER PARTIAL CONVERSION OF POLYMERIZABLE MONOMERIC MATERIAL TO POLYMERIC MATERIAL. 